During surgical repair of an organ or other body part, the surgeon typically makes an incision to open the organ. Upon closure of the surgical wound, sutures are placed in the various layers of tissue to draw the two edges of the wound together so that the healing process can reform a smooth and competent surface. However, sutures often tear through the tissue if they are subjected to stress, thus damaging the surgical closure of the wound. It would be desirable in many instances to have a means for lending permanent support to strengthen and support the wall of the organ into which the surgical incision has been placed. Alternatively, in many instances it would be preferred to have a biodegradable suture guide.
In many cases, the incision is not a straight line, but is shaped to conform to an anatomical requirement, making it difficult for the surgeon to balance the tension on the sutures to form the desired shape. In a number of instances the suture line is substantially curvilinear and it is of utmost importance that the suture line maintain a predetermined dimension. For example, when two blood vessels, or other vessels, such as intestines, are sutured together, the need exists for some means of preventing the suture line from constricting the vessel so as to create a potential point of blockage. Similar problems arise during bowel and bronchial resection. As another example, when the surgeon is reducing the size of a stomach by surgical means, the need exists for a means to assure that the reshaped organ will have a particular circumferential dimension and that the pleats used to reduce the size of the organ are evenly distributed so as to avoid formation of areas of reduced flexibility along the suture line. In other situations, such as in cosmetic surgery, the surgeon may desire to assure that the suture line is limited to a predetermined length.
In all of these situations, it is desirable to use a suture guide to aid the surgeon in achieving the desired dimension of the surgical closure and/or to rigidly support the area where the sutures are placed, thus avoiding the danger that the sutures will tear through the tissue or that the suture line will act like a draw string and undesirably bunch up the tissue.
These problems are particularly acute in the surgical procedure known as annuloplasty wherein any of a number of types of prostheses have been used in surgical correction of deformed mitral or bicuspid heart valves.
Diseases and certain natural defects to heart valves can impair the functioning of the cusps of the valves in preventing regurgitation of blood from the ventricle into the atrium when the ventricle contracts. For example, rheumatic fever and bacterial inflammations of the heart tissue can distort or dilate the valvular annulus, thus resulting in displacement of the cusps away from the center of the valve and causing leakage of blood during ventricle contraction.
Two techniques, generally known as annuloplasty, are used to reshape the distended and/or deformed valve annulus. In the technique known as "plication," the circumference of the valve annulus is reduced by implanting a rigid or semi-rigid prosthetic ring of reduced circumference about the base of the annulus while the annulus is pleated to reduce its circumference to that of the ring. In the technique known as "reconstruction", the circumference of the annulus is not reduced, but the annulus is restructured into an elongate shape. To accomplish this goal, a rigid or semi-rigid ring having the same circumference as the annulus but in an elongate or elliptical shape is surgically implanted about the base of the valve. Both plication and restructuring are intended to eliminate the gap in the closure of the distended valve by bringing back together the tips of the valve cusps.
Many different types of prostheses have been developed for use in annuloplasty surgery. In general, prostheses are annular or partially annular shaped members that fit about the base of the valve annulus. Initially the prostheses were designed as rigid frame members, or "rings", of metallic or other rigid materials that flex little, if at all, during the normal opening and closing of the valve. Since a normal heart valve annulus continuously flexes during the cardiac cycle, a rigid ring prosthesis interferes with this movement and thereby restricts movement of the valve itself. Sutures used to implant rigid ring prostheses consequently undergo stresses sufficient to tear the sutures loose. Examples of rigid annuloplasty ring prostheses are disclosed in U.S. Pat. Nos. 3,656,185, issued to Carpentier on Apr. 18, 1972; and 4,164,046, issued to Cooley on Aug. 14, 1979.
Others have suggested the use of completely flexible annuloplasty ring prostheses. Examples of completely flexible ring prostheses are disclosed in U.S. Pat. No. 4,290,151, issued to Massana on Sep. 22, 1981, and are discussed in the articles of Carlos D. Duran and Jose Luis M. Ubago, "Clinical and Hemodymanic Performance of a Totally Flexible Prosthetic Ring for Atrioventricular Valve Reconstruction", 5 Annals of Thoracic Surgery, (No. 5), 458-463, (Nov. 1976) and M. Puig Massana et al, "Conservative Surgery of the Mitral Valve Annuloplasty on a New Adjustable Ring", Cardiovascular Surgery 1980, 30-37, (1981).
Flexible prostheses generally include an inner support member formed from a flexible material. This support member is wrapped in woven, biocompatible cloth material. Realignment of the valve cusps during opening and closing of the valve is obtained by the proper suturing of the ring about the valve annulus. However, completely flexible ring prostheses provide almost no support to the suture area during the precarious implant procedure. Even though the surgeon attempts to evenly distribute the sutures along the periphery of the valvular annulus, during implant the drawstring effect of the sutures tends to bunch the material covering the flexible ring so that the sutures also bunch together at localized areas around the ring. This phenomenon, known as multiple plications in the heart valve annulus, causes rigid areas around the annulus. Thus, the flexible ring actually ends by imparting areas of rigidity and thereby distorts the valve annulus during the opening and closing of the valve despite the desired reduction in circumference of the valvular annulus.
To overcome some of the drawbacks of rigid ring prostheses, still further types of annuloplasty prostheses have been designed to allow for adjustment of the ring circumference, either by the surgeon during implant, or automatically as the implanted ring moves during the opening and closing of the valve. This type of adjustable prosthesis is typically designed in combination with a rigid, or at least partially rigid, frame.
An example of a self adjusting ring prosthesis is taught in U.S. Pat. No. 4,489,446, issued to Reed on Dec. 25, 1984. To provide for self adjustment of the prosthetic annulus, two reciprocating rigid metal pieces form the frame. U.S. Pat. Nos. 4,602,911, issued to Ahmadi et al. and 4,042,979, issued to Angell on Aug. 23, 1977, provide further adjustable ring protheses having a mechanism for adjusting the circumference of the ring. But due to rigidity of the frame members, the self-adjusting prostheses do not overcome many of the disadvantages of other types of rigid ring prostheses.
U.S. Pat. No. 4,055,861, issued to Carpentier on Nov. 1, 1977, teaches an annuloplasty ring prosthesis having a flexibility between the completely flexible rings discussed above and the various types of rigid ring. The ring of Carpentier is deformable to an equal degree and simultaneously in all directions and preferably has the elasticity of an annular bundle of 2 to 8 turns of a cylindrical bristle of poly(ethylene terephthalate).
While rigid and semi-rigid annuloplasty rings eliminate the bunching caused by flexible rings, the restrictive nature of such rings is generally detrimental to the valve's ability to open and close normally. It thus remains an object of the invention to provide a surgical means for reshaping a deformed or dilated heart valve annulus having none of the above described drawbacks associated with known annuloplasty ring prostheses.
For use in annuloplasty of heart valves, as in other applications, it is desirable that a suture guide be entirely flexible, light weight, and compliant while having sufficient strength to withstand stress placed upon the sutures sewn through and around it. However, an entirely flexible suture guide cannot prevent bunching of the tissue in the draw-string effect described above and thus cannot assure that the suture line and the tissue into which it is placed will maintain any desired dimension, for example, a desired circumference. Therefore the need exists for a means of temporarily providing rigidity and fixed dimension to the suture guide during the surgery, but rendering the suture-guide freely flexible once the surgery has been accomplished.